Catheters are widely used in medical procedures, since they provide access to internal bodily passages and cavities for both diagnostic and therapeutic purposes without surgery. Catheters have proved valuable over the years for use in regions of the body such as the heart and coronary arteries, the brain, and the genito-urinary tract.
A critical procedure associated with the use of medical catheters is the insertion of the catheter into the body and the placement of the catheter tip at the appropriate location. Precise placement of the catheter tip is often critical to the success of the function the catheter is intended to perform, since the function must often be directed to a highly localized region of internal tissue while avoiding areas which are immediately adjacent. In addition, bodily passages are often of a very small diameter, and the interior wall of the passage is often delicate and susceptible to puncture. Steering capability is important, for example, in cardiovascular surgery when catheters are used as an alternative to bypass surgery to selectively remove plaque from arteries. The use of a catheter in these procedures offers significant benefits in terms of lower cost and lower risk. Steering capability is of particular importance in procedures involving peripheral arteries where plaque or thrombi are to be removed. In obstetrics and gynecology, catheters can be used in conjunction with dilatation and curettage procedures for the selective removal of excessive tissue and cyst growth, and directional control is important here as well. The same is true for the use of catheters for the delivery of site-specific treatments for ovarian cancer. Directional control is also important in urology procedures involving catheters. Examples of such procedures are the selective removal of prostate cancer and the treatment of urinary tract blockages infections. In certain oncology procedures, accurately guided catheters can be used for the selective removal of malignant tissue without affecting critical healthy tissue located nearby, and for improved biopsy methods, where it is important to reduce the incidence of trauma in healthy tissue. In neurosurgery, catheters can be used for the removal of intracranial hematomas and similar procedures, and precise directional control of the catheters is critical. In radiology, close directional control provides imaging and mapping catheters with active stabilization within the cardiac chamber. In internal body procedures in general, guided catheters are useful for such procedures as fluid aspiration to relieve abscesses and localized drug delivery. Other procedures and applications where steering capability is important will be readily apparent to the experienced medical practitioner.
Steering mechanisms have been devised for directing the distal tip of the catheter in a desired direction by remote control from the proximal end. One such mechanism includes a series of wires running the length of the catheter body on either side of its central axis and terminating in shims or thin strips at the distal end of the catheter. The operator steers the catheter by applying tension to one shim relative to the other, thereby causing the distal end to curve in the direction of the wire to which tension has been applied. The wires and the mechanism at the proximal end for selectively applying tension are unwieldy, however, and susceptible to breakage. Furthermore, they offer limited directional choice without twisting the entire catheter to achieve angular adjustments relative to the catheter axis.
Guidewires are widely used to assist in the placement of catheters in locations which are particularly difficult to reach. A guidewire is typically of very narrow diameter to fit within the lumen of a catheter. This permits the operator to slide the catheter over the guidewire after first directing the guidewire to the appropriate location. It also permits the operator to remove one catheter and replace it with another without removing the guidewire and hence without the cumbersome procedure of independently relocating the catheter tip to the region of interest. The steering of a guidewire is generally accomplished by constructing the guidewire to include a slight curvature at its distal tip, the tip being resilient in construction to resume the curvature when relaxed. This enables the operator to direct the guidewire tip laterally into branches of the vessel. To do this, however, the operator must rotate the guidewire from the proximal end so that the tip curves in the desired direction.